Anatomy of External ear

 INTRODUCTION 

 

The ear is an organ of hearing. It is also concerned with maintaining the equilibrium of the body  One hears with the ears. The centre for hearing is in the temporal lobe of the brain above the ear

It consists of three parts:

1. External ear 
2. Middle ear 
3. Internal ear 

EXTERNAL EAR 

Features of external ear :

external consist of ear pinna, the external acoustic meatus and external auditory canal and the tympanic membrane 

AURICLE (pinna):

it is made up of a single plate of elastic cartilage which is lined with skin on both sides.

the lowest part of the auricle is the lobule, it is soft and made up of fibrofatty tissue.

the auricle is divided into different parts :

1. helix
2. anti-helix
3. concha
4. tragus
5. scaphoid fossa 

nerve supply :

 Auriculotemporal nerve - upper 2/3rd of lateral surface  

Great auricular nerve - lower 1/3 of lateral surface and medial surface 

Lesser occipital nerve - upper two-thirds of the medial surface 

Auricular branch of the vagus nerve - root of auricle 

Facial nerve - auricular muscles 

 

blood supply :

blood supply is through posterior auricular and superficial temporal artery 

lymph drainage: the preauricular and postauricular lymph nodes 

EXTERNAL ACOUSTIC MEATUS 

features of external acoustic meatus :

• conducts soundwave from concha to the tympanic membrane.
• The canal is S-shaped

• 24 mm long
• 16 mm is bony (medial 2/3rd)
• The bony part is formed by the tympanic plate of the temporal bone

• 8 mm is cartilaginous (lateral 1/3 rd)
• it is filled with fibrous tissue 
• the anterior wall and the floor are longer than the posterior wall and roof 

• The narrowest point, the isthmus, lies about 5 mm from the tympanic membrane

• The lining skin is adherent to the perichondrium and contains hairs, sebaceous glands, and ceruminous or wax glands (modified sweat glands)

 blood supply:

 

Outer part of canal - superficial temporal and posterior auricular arteries 

Inner part of canal - deep auricular branch of maxillary artery 

nerve supply : 

aurictemporal nerve - skin in the anterior half of meatus 

auricular branch of vagus  - skin in posterior half  

TYMPAIC MEMBRANE 

features : 

• thin and translucent 
• 9 x 10 mm, oblique at an angle of 55 degrees 

• OUTER SURFACE
• lined by thin skin 
• it is concave 

• INNER SURFACE 
• has attachment to the handle of the malleus 
• it is convex 
• point of maximum convexity at the tip of malleus is called umbo
• the greater part of the tympanic membrane is tightly stretched is called the pars tensa.

• the part between the two malleolar folds is loose and is called the pars flaccida.
  

STRUCTURE :

tympanic membrane is composed of three layers :

1. outer cuticular layer of skin 

2. middle fibrous layer 

    -  made up of superficial radiating fibres and deep circular fibres.       - The circular fibres are minimal at the centre and maximal at the periphery.

The fibrous layer is replaced by loose areolar tissue in the pars flaccida

3. inner mucosa layer 

    -lined by a low ciliated columnar epithelium.

blood supply :

outer surface - deep auricular branch of maxillary artery 

inner surface - anterior tympanic branch of maxillary artery 

                        - posterior tympanic branch of auricular artery 

venous drainage:

outer surface - external jugular vein 

inner surface - transverse sinus and venous plexus around the auditory tube

lymph drainage:  preauricular and retropharyngeal lymph nodes 

nerve supply:

• outer surface 
• anteroinferior by auricuotemporal nerve 
• posterosuperior by auricular branch of the vagus nerve 
• inner surface 
• tympanic branch of the glossopharyngeal nerve through tympanic plexus